1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus such as a copier, facsimile device or printer, and more particularly to a development apparatus that employs a two-component developer comprising a toner and a magnetic carrier and an image forming apparatus employing the same.
2. Description of the Related Art
In conventionally known development apparatuses in which a two-component developer is employed the developer is circulated by, while the developer is conveyed in the width direction of a developer carrier, the provision of a supply conveyance path for supplying the developer to the developer carrier, and an agitation carrier path for agitating the developer while conveying it in the reverse direction to the supply conveyance path. In development apparatuses such as this, when recovery developer that has been supplied to the developer carrier has passed through the development region is recovered in the supply conveyance path, a mixing of the developer that has passed through the development region from which toner has been consumed and the developer in the supply conveyance path in the supply conveyance path occurs. There is a problem associated therewith in that, because the quantity of developer that has passed through the development region increases toward the downstream side of the supply conveyance path, the toner density of the developer supplied to the developer carrier drops toward the downstream side in the direction of conveyance of the supply conveyance path. A drop in the toner density of the developer supplied to the developer carrier results in a drop in the image density during development and, accordingly, irregularities in image density in which the image density between the upstream side and the downstream side in the direction of conveyance of the conveyance path for supplying developer to the developer carrier differs.
On the other hand, when recovery developer is recovered in the agitation conveyance path, the greater the amount of developer recovered at the downstream side in the direction of conveyance of the agitation conveyance path the shorter the agitation time. Because the developer that has arrived at the end part on the downstream side in the direction of conveyance of the agitation conveyance path is delivered to the end part on the upstream side in the direction of conveyance of the supply conveyance path, the developer recovered on the downstream side in the direction of conveyance of the agitation conveyance path is immediately supplied to the supply conveyance path. As a result, even if a replenishment of the toner is performed to maintain a suitable toner density in accordance with the output image, problems of non-uniformity of image density and a drop in image density and so on occur due to inadequate agitation of the developer and non-uniformity of the toner charge amount.
Problems such as these that have their origin in the recovery of the recovery developer in the supply conveyance path or agitation conveyance path can be resolved by, as in the development apparatus described in Japanese Unexamined Patent Application No. H11-167260, the provision of a recovery conveyance path for recovery of the recovery developer separate to the supply conveyance path and agitation conveyance path. This development apparatus comprises a supply conveyance path for, while a developer is being conveyed, supplying it to a developer carrier, and a recovery conveyance path for recovering a recovery developer while conveying it in the same direction as the supply conveyance path. The development apparatus further comprises an agitation conveyance path for agitating surplus developer that has arrived at the downstream end in the direction of conveyance of the supply conveyance path and the recovery developer that has arrived at the downstream end in the direction of conveyance of the recovery conveyance path. The supply conveyance path, recovery conveyance path and agitation conveyance path are each partitioned by partition members. An opening through which the agitated developer is delivered to the supply conveyance path is provided in a partition member with the supply conveyance path at the end part on the downstream side of the agitation conveyance path. In addition, an opening through which the surplus developer is delivered to the agitation conveyance path is provided in a partition member with the agitation conveyance path at the end part on the downstream side of the supply conveyance path, and an opening through which recovery developer is delivered to the agitation conveyance path is provided in a partition member with the agitation conveyance path at the end part on the downstream side of the recovery conveyance path.
By implementing the functions of supply and recovery of the developer to the developer carrier separately in this way, the toner density of the developer supplied to the developer carrier can be made constant and a generation of density irregularities can be prevented. In addition, by implementing the functions of agitation and recovery of the developer separately, thorough agitation of the developer is possible and image density can be stabilized.
In a conventional development apparatus comprising three separate developer conveyance paths for supply, recovery and agitation of the developer, the openings through which the supply conveyance path is linked with the agitation conveyance path at the end part on the upstream side and the end part on the downstream side of the supply conveyance path are provided on the outer side of a development region width which refers to the width of the development region in which a developer carrier supplies toner to a latent image carrier. Accordingly, the length in the direction of conveyance of at least the supply conveyance path and agitation conveyance path is longer than the developer carrier by the length occupied by these openings and the apparatus is increased in size to that extent.
In addition, in a conventional apparatus comprising separate developer conveyance paths for supply, recovery and agitation of the developer, the opening through which the agitation conveyance path is linked with the end part on the downstream side of the recovery conveyance path is provided on the outer side of the width in the axial direction of the developer carrier. Accordingly, the length in the direction of conveyance of at least the recovery conveyance path and agitation conveyance path is longer than the developer carrier by the length occupied by this opening and the apparatus is increased in size to that extent.
Furthermore, in a conventional apparatus comprising separate developer conveyance paths for supply, recovery and agitation of the developer, a toner replenishment port for replenishing toner to the developer conveyance path is provided on the outer side of the width in the axial direction of the developer carrier. Accordingly, the length in the direction of conveyance of at least the developer conveyance path comprising the toner replenishment port of the developer conveyance paths is longer than the developer carrier by the length occupied by this toner replenishment port and the apparatus is increased in size to that extent.
Technologies relating to the present invention are disclosed in, e.g.,
Japanese Unexamined Patent Application No. H07-013424
Japanese Unexamined Patent Application No. H10-123817 and
Japanese Unexamined Patent Application No. 2001-290368